In general, an explosive is a material that reacts chemically to generate gases at high temperatures and pressures. The expansion of these gases is used to produce a wide range of effects including destructive blast effects, propellant effects and gas generation. These explosive materials are ignited by smaller charges, i.e. primer charges, contained within primers, which are in turn ignited by an initiator containing a small initiator charge.
Initiators are typically used to prime a priming composition located within a primer. The priming composition is used to ignite the main charge in an ordinance, shell, rocket, actuator or gas generator. In ammunition, the main charge acts as a propellant charge to propel a projectile or shell. In a gas generator, the main charge is used to generate gas, for example, for use in an airbag or seatbelt tightener. The main charge is typically an energetic material such as an energetic pyrotechnic chemical or black powder. The initiator includes an initiator charge that is ignited by either electricity or percussion, and the initiator charge ignites the primer charge, which ignites the main charge. The initiator, the primer and the main charge are disposed in various housings that are typically connected together so as to be placed in the necessary contacting arrangement for proper functioning of the pyrotechnic device.
Percussion initiators use a physical force to ignite either the initiator charge or the primer charge. An electrical initiator typically contains two contact pins. Between the two contact pins a resistor element is disposed, for example a metal film element or an incandescing wire. An initiator charge adjoins the resistor element. Upon application of current to the contact pins, the initiator charge ignites as a result of the high temperature of the resistor element. The ignited initiator charge ignites the primer charge. Therefore, the electrical initiator is the start of the ignition sequence in an electric primer.
Initiators, primers, and main charges are all exposed to both high temperatures and pressures resulting from the ignition of the energetic material contained therein. These high temperatures and pressures can result in flaws within the various components including the primer, initiator and main charge, and of the seals between these various elements, including conventional pressure fit seals. These flaws include potential escape paths for the hot gases generated by the energetic materials in addition to locations for burn throughs. Therefore, an arrangement of initiators and primers is desired that eliminates potential flaws resulting from the ignition of the initiator charges, primer charges, or main charges. Accordingly, Applicant has developed a novel seal arrangement using threads among the components to minimize the damage due to escaping hot gases and burn throughs.